1. Field of the Invention
The present invention relates to a movable platen support mechanism used in an injection molding machine provided with a movable platen, stationary platen, rear platen, die clamping mechanism, and linear guide unit for axially guiding the movable platen.
2. Description of the Related Art
As shown in FIG. 11, an injection molding machine usually comprises a die clamping unit 100 and an injection unit 200, which are located on a base frame 300. The die clamping unit 100 includes a movable platen 1, stationary platen 9, rear platen 12, and toggle mechanism 13. A plurality of tie-bars 14 are mounted between the stationary platen 9 and the rear platen 12 so as to penetrate the movable platen 1. The tie-bars 14 are slidable relative to the movable platen 1. The stationary platen 9 is fitted with a stationary die (not shown), and the movable platen 1 with a movable die (not shown).
A pair of linear guide rails 11 are mounted on the base frame 300, and linear guide blocks 5 to which the guide mounting block 2 is secured are placed on the guide rails 11. The linear guide blocks 5 are movable longitudinally relative to the guide rails 11. The movable platen 1 is secured to the linear guide blocks 5 by bolts (not shown) or the like with the aid of the guide mounting block 2. The toggle mechanism 13 is powered by a movable platen driving servomotor (not shown). As the toggle mechanism 13 is driven, the movable platen 1 approaches or withdraws from the stationary platen 9. As the movable platen 1 moves in this manner, the linear guide blocks 5 move on the guide rails 11 longitudinally relative thereto. For example, Japanese Patent Application Laid-Open No. 9-262884 discloses a technique in which a linear guide is used to guide a movable platen in a die clamping mechanism of an injection molding machine, in order to improve the die opening/closing accuracy.
If the linear guide is used to guide the movable platen, as described above, a load produced by the deformation of the movable platen acts on the linear guide, thereby greatly affecting the life performance of the guide. Some of measures to counter this phenomenon are proposed in the following Japanese patent publications.
Japanese Patent Application Laid-Open No. 8-258103 discloses a platen structure that can suppress deflection.
Japanese Patent Application Laid-Open No. 2006-272558 discloses a technique in which an expensive material with a low linear expansion coefficient is used for a platen and a platen support member.
Japanese Patent Application Laid-Open No. 2003-71894 discloses a mechanism in which spring elements are vertically attached to the lower end portion of a movable platen, as a mechanism that can absorb deformation of the movable platen.
Japanese Patent Application Laid-Open No. 2004-330449 discloses a mechanism in which buffer members (spring elements or fluid-pressure cylinders) are arranged vertically and horizontally between a movable platen and a linear guide unit, as a mechanism that can absorb vertical and horizontal deformations of a movable platen.
If the linear guide is used to guide the movable platen, as mentioned before, a load produced by the deformation of the movable platen acts on the linear guide, so that the life performance of the guide is greatly affected. The deformation of the movable platen is attributable to deflection by a die clamping force and thermal expansion caused by die temperature control.
The deflection by the die clamping force can be reduced by the technique disclosed in Japanese Patent Application Laid-Open No. 8-258103.
Further, the thermal expansion due to die temperature control can be reduced by the technique disclosed in Japanese Patent Application Laid-Open No. 2006-272558. In this case, however, an expensive material with a low linear expansion coefficient needs to be used for a platen, such as a movable platen, and a platen support member, thus entailing an increase in the manufacturing cost of an injection molding machine.
According to the technique disclosed in Japanese Patent Application Laid-Open No. 2003-71894, the spring elements are mounted vertically, so that they cannot absorb horizontal deformation of the movable platen. Further, the spring elements are located between a guide mounting block and mounting bolts, so that the posture of the platen does not change if shims are fitted to bolt seating surfaces. Thus, this technique is not applicable to parallelism adjustment.
According to the technique disclosed in Japanese Patent Application Laid-Open No. 2004-330449, the buffer members are mounted vertically and horizontally, so that the posture of the movable platen is unstable and requires support by tie-bars. Thus, the effect of the linear guide unit to improve the die opening/closing accuracy is small. Since the adjustment of the parallelism of the platen is not taken into consideration, moreover, this technique is not applicable to the parallelism adjustment.